Multi-stage bubble column humidifier

ABSTRACT

A feed liquid flows into a second-stage humidifier chamber to form a second-stage humidifier bath. A first remnant of the feed liquid from the second-stage humidifier chamber then flows into a first-stage humidifier chamber to form a first-stage humidifier bath having a temperature lower than that of the second-stage bath. A second remnant of the feed liquid is then removed from the first-stage humidifier. Meanwhile, a carrier gas is injected into and bubbled through the first-stage humidifier bath, collecting a vaporizable component in vapor form from the first remnant of the feed liquid to partially humidify the carrier gas. The partially humidified carrier gas is then bubbled through the second-stage humidifier bath, where the carrier gas collects more of the vaporizable component in vapor form from the feed liquid to further humidify the carrier gas before the humidified carrier gas is removed from the second-stage humidifier chamber.

RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.13/916,038, filed 12 Jun. 2013 (now U.S. Pat. No. 9,120,033 B2, issued 1Sep. 2015), the entire contents of which are incorporated herein byreference.

BACKGROUND

In this century, the shortage of fresh water will surpass the shortageof energy as a global concern for humanity; and these two challenges areinexorably linked, as explained, for example, in the “Special Report onWater” in the 20 May 2010 issue of The Economist. Fresh water is one ofthe most fundamental needs of humans and other organisms; each humanneeds to consume a minimum of about two liters per day. The world alsofaces greater freshwater demands from farming and industrial processes.

The hazards posed by insufficient water supplies are particularly acute.A shortage of fresh water may lead to a variety of crises, includingfamine, disease, death, forced mass migration, cross-regionconflict/war, and collapsed ecosystems. Despite the criticality of theneed for fresh water and the profound consequences of shortages,supplies of fresh water are particularly constrained. 97.5% of the wateron Earth is salty, and about 70% of the remainder is locked up as ice(mostly in ice caps and glaciers), leaving only a fraction of all wateron Earth as available fresh (non-saline) water.

Moreover, the earth's water that is fresh and available is not evenlydistributed. For example, heavily populated countries, such as India andChina, have many regions that are subject to scarce supplies. Furtherstill, the supply of fresh water is often seasonally inconsistent.Meanwhile, demands for fresh water are tightening across the globe.Reservoirs are drying up; aquifers are falling; rivers are dying; andglaciers and ice caps are retracting. Rising populations increasedemand, as do shifts in farming and increased industrialization. Climatechange poses even more threats in many regions. Consequently, the numberof people facing water shortages is increasing. Naturally occurringfresh water, however, is typically confined to regional drainage basins;and transport of water is expensive and energy-intensive. Nevertheless,many of the existing processes for producing fresh water from seawater(or from brackish water or contaminated waste streams) require massiveamounts of energy. Reverse osmosis (RO) is currently the leadingdesalination technology. In large-scale plants, the specific electricityrequired can be as low as 4 kWh/m³ at 30% recovery, compared to thetheoretical minimum of around 1 kWh/m³; smaller-scale RO systems (e.g.,aboard ships) are less efficient.

Other existing seawater desalination systems includethermal-energy-based multi-stage flash (MSF) distillation, andmulti-effect distillation (MED), both of which are energy- andcapital-intensive processes. In MSF and MED systems, however, themaximum brine temperature and the maximum temperature of the heat inputare limited in order to avoid calcium sulfate, magnesium hydroxide andcalcium carbonate precipitation, which leads to the formation of softand hard scale on the heat transfer equipment.

Humidification-dehumidification (HDH) desalination systems include ahumidifier and a dehumidifier as their main components and use a carriergas (e.g., air) to communicate energy between the heat source and thebrine. A simple version of this technology includes a humidifier, adehumidifier, and a heater to heat the seawater stream. In thehumidifier, hot seawater comes in direct contact with dry air, and thisair becomes heated and humidified. In the dehumidifier, the heated andhumidified air is brought into (indirect) contact with cold seawater andgets dehumidified, producing pure water and dehumidified air. As withMSF and MED systems, precipitation of scaling components can occurwithin the system with consequent damage if the temperature rises toohigh.

Another approach, described in U.S. Pat. No. 8,119,007 B2 (A. Bajpayee,et al.), uses directional solvent that directionally dissolves water butdoes not dissolve salt. The directional solvent is heated to dissolvewater from a salt solution into the directional solvent. The remaininghighly concentrated salt water is removed, and the solution ofdirectional solvent and water is cooled to precipitate substantiallypure water out of the solution.

Some of the present inventors were also named as inventors on thefollowing patent applications that include additional discussion of HDHand other processes for purifying water: U.S. application Ser. No.12/554,726, filed 4 Sep. 2009 (now U.S. Pat. No. 8,465,006 B2); U.S.application Ser. No. 12/573,221, filed 5 Oct. 2009 (now U.S. Pat. No.8,252,092 B2); U.S. application Ser. No. 13/028,170, filed 15 Feb. 2011now U.S. Pat. No. 8,647,477 B2); and U.S. application Ser. No.13/241,907, filed 23 Sep. 2011 (now U.S. Pat. No. 9,072,984 B2); andU.S. application Ser. No. 13/550,094, filed 16 Jul. 2012 (now U.S. Pat.No. 8,496,234 B1).

SUMMARY

Methods and apparatus for separating a liquid (e.g., pure water) from afeed liquid (e.g., seawater, brackish water, waste water, or flowback orproduced water) in a cost-efficient manner are described herein. Variousembodiments of the methods and apparatus may include some or all of theelements, features and steps described below.

In a method for humidification of a vaporizable component from a feedliquid, the feed liquid including the vaporizable component flows into asecond-stage humidifier chamber to form a second-stage humidifier bathat a second humidification temperature. A first remnant of the feedliquid from the second-stage humidifier chamber then flows into afirst-stage humidifier chamber to form a first-stage humidifier bath ata first humidification temperature, wherein the first humidificationtemperature is lower than the second humidification temperature. Asecond remnant of the feed liquid is then removed from the first-stagehumidifier chamber.

Meanwhile, a carrier gas is injected into the first-stage humidifierbath in the first-stage chamber and bubbled through the first-stagehumidifier bath, where the carrier gas collects the vaporizablecomponent in vapor form from the first remnant of the feed liquid topartially humidify the carrier gas with the vaporizable component. Thepartially humidified carrier gas is then directed from the firsthumidifier chamber into the second-stage humidifier bath in thesecond-stage humidifier chamber and bubbled through the second-stagehumidifier bath, where the carrier gas collects more of the vaporizablecomponent in vapor form from the feed liquid to further humidify thecarrier gas with the vaporizable component; the humidified carrier gasis then removed from the second-stage humidifier chamber.

In a multi-stage bubble-column humidification apparatus, a feed-liquidsource contains a feed liquid; and a second-stage humidifier chamber isconfigured to receive the feed liquid from the feed-liquid source andcontains a bubble distributor. Furthermore, a first-stage humidifierchamber is configured to receive a remnant of the feed liquid from thesecond-stage humidifier chamber and contains a bubble distributor. Acarrier-gas source contains a carrier gas, wherein the first-stagehumidifier chamber is configured to receive the carrier gas from thecarrier-gas source and to disperse the carrier gas through the bubbledistributor of the first-stage humidifier chamber, and wherein thesecond-stage humidifier chamber is configured to receive the carrier gasfrom the first-stage humidifier chamber and to disperse the carrier gasthrough the bubble distributor of the second-stage humidifier chamber.

The multi-stage bubble-column humidifier described herein can substitutefor the packed-bed heat exchanger previously used inhumidification-dehumidification systems to efficiently humidify dry air.Advantages that may be provided by embodiments of the methods andapparatus described herein include reduced-cost dehumidification, asboth the equipment cost and the cost of energy for operation can bereduced. In particular the energy for humidification can be directlyprovided by the feed liquid in the humidification chambers.Additionally, very high heat and mass transfer rates in the multi-stagehumidifier enable the design and use of a very small humidificationdevice. Further still, multi-extraction can be used in the multi-stagebubble column to further increase heat recovery.

Additionally, the methods described herein can be used to advantageouslyextract water from contaminated waste streams (e.g., from oil and gasproduction) both to produce fresh water and to concentrate and reducethe volume of the waste streams, thereby reducing pollution andcontamination and reducing costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional illustration of an embodiment of amulti-stage bubble-column humidifier.

FIG. 2 is a sectional illustration of an embodiment of a first-stagehumidification chamber in the multi-stage bubble-column humidifier.

FIG. 3 is a schematic sectional illustration of a multi-stage,single-column humidification-dehumidification (HDH) system.

FIG. 4 is a schematic sectional illustration of a multi-stage,single-column HDH system including multi-extraction conduits for thefeed liquid and carrier gas.

In the accompanying drawings, like reference characters refer to thesame or similar parts throughout the different views. The drawings arenot necessarily to scale, emphasis instead being placed uponillustrating particular principles, discussed below.

DETAILED DESCRIPTION

The foregoing and other features and advantages of various aspects ofthe invention(s) will be apparent from the following, more-particulardescription of various concepts and specific embodiments within thebroader bounds of the invention(s). Various aspects of the subjectmatter introduced above and discussed in greater detail below may beimplemented in any of numerous ways, as the subject matter is notlimited to any particular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes.

Unless otherwise defined, used or characterized herein, terms that areused herein (including technical and scientific terms) are to beinterpreted as having a meaning that is consistent with their acceptedmeaning in the context of the relevant art and are not to be interpretedin an idealized or overly formal sense unless expressly so definedherein. For example, if a particular composition is referenced, thecomposition may be substantially, though not perfectly pure, aspractical and imperfect realities may apply; e.g., the potentialpresence of at least trace impurities (e.g., at less than 1 or 2%) canbe understood as being within the scope of the description; likewise, ifa particular shape is referenced, the shape is intended to includeimperfect variations from ideal shapes, e.g., due to manufacturingtolerances. Percentages or concentrations expressed herein can representeither by weight or by volume.

Although the terms, first, second, third, etc., may be used herein todescribe various elements, these elements are not to be limited by theseterms. These terms are simply used to distinguish one element fromanother. Thus, a first element, discussed below, could be termed asecond element without departing from the teachings of the exemplaryembodiments.

Spatially relative terms, such as “above,” “below,” “left,” “right,” “infront,” “behind,” and the like, may be used herein for ease ofdescription to describe the relationship of one element to anotherelement, as illustrated in the figures. It will be understood that thespatially relative terms, as well as the illustrated configurations, areintended to encompass different orientations of the apparatus in use oroperation in addition to the orientations described herein and depictedin the figures. For example, if the apparatus in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term, “above,” may encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (e.g., rotated90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Further still, in this disclosure, when an element is referred to asbeing “on,” “connected to” or “coupled to” another element, it may bedirectly on, connected or coupled to the other element or interveningelements may be present unless otherwise specified.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of exemplary embodiments.As used herein, singular forms, such as “a” and “an,” are intended toinclude the plural forms as well, unless the context indicatesotherwise. Additionally, the terms, “includes,” “including,” “comprises”and “comprising,” specify the presence of the stated elements or stepsbut do not preclude the presence or addition of one or more otherelements or steps.

An embodiment of a multi-stage bubble-column humidifier 12 with fourstages is illustrated FIG. 1. In other embodiments, more or fewerhumidification stages can be linked in series, as described below, forcarrying out the humidification process. Feed liquid containingdissolved components is fed from a feed-liquid source 14 (e.g., anocean, pond or storage tank) into a fourth-stage humidification chamber22 of the humidifier 12, where the feed liquid forms a bath 24 containedwithin the chamber 22. In a first embodiment, the feed liquid is fedinto the fourth-stage humidification chamber 22 at a temperature of 70°C. A vaporizable component (e.g., water) of the feed liquid is vaporizedinto a carrier gas that bubbles through the bath 24, as described below.

A remnant of the feed liquid (with further-concentrated dissolvedcomponents) is fed from the fourth-stage humidification chamber 22 via aconduit 26 into a third-stage humidification chamber 20, in which theremnant of the feed liquid forms another bath 24 through which thecarrier gas is bubbled. In the first embodiment, the remnant of the feedliquid is fed into the third-stage humidification chamber 20 at atemperature of 62° C. in this embodiment; the temperature of theremaining feed is reduced from stage-to-stage, in part, via the energyused for vaporization of the vaporizable component from the feed liquidat each stage into the carrier gas.

In turn, a remnant of the feed liquid (with still-further-concentrateddissolved components) is fed from the third-stage humidification chamber20 via a conduit 28 into a second-stage humidification chamber 18, inwhich the remnant of the feed liquid forms another bath 24 through whichthe carrier gas is bubbled. The remnant of the feed liquid is fed intothe second-stage humidification chamber 18 at a temperature of 56° C. inthis embodiment.

Finally, a remnant of the feed liquid (with still-further-concentrateddissolved components) is fed from the second-stage humidificationchamber 18 via a conduit 30 into a first-stage humidification chamber16, in which the remnant of the feed liquid forms another bath 24through which the carrier gas is bubbled. In the first embodiment, theremnant of the feed liquid is fed into the first-stage humidificationchamber 16 at a temperature of 51.3° C. in this embodiment. The remnantof the feed liquid, which can now be in the form of a cold brine, can beremoved from the first-stage humidification chamber (e.g., at atemperature of 45.7° C. in this embodiment) via a conduit 32 to a brinestorage reservoir 33. Accordingly, the temperature of the feed liquidcan drop by, e.g., about 5%-15% across each stage.

Meanwhile, a cool, dry carrier gas is bubbled through the bath 24 ofeach stage to remove the vaporized component from the baths 24 (as shownin FIG. 2), where flow of the carrier gas between the chambers is shownwith arrows 36 in FIG. 1. The carrier gas can be, e.g., air, and it caninitially be fed into the first-stage humidification chamber 16 from acarrier-gas reservoir 35 pressurized by a blower pump 34 feeding intothe reservoir 35. The carrier gas fills a lower gas region 38 inside thefirst-stage humidification chamber 16 and flows through a bubbledistributor (here, a sparger plate) 40 into the bath 24 in the form ofbubbles 42 (as shown in FIG. 2), where the carrier gas is heated andhumidified (with the heat and humidification provided by the feedliquid). The vaporizable component (e.g., water) of the feed liquidvaporizes into the bubbles 42 at the gas-liquid interface of the bath 24and bubbles 42. The bubbles 42 flow up through the bath 24, gainingthermal energy and the vaporizable component (in vapor form) from thebath 24 until the carrier gas enters the top gas region 44 above thebath 24 and then out the gas conduit 46 to the second-stagehumidification chamber 18. The remaining humidification chambers 18, 20and 22 have a design and operation similar to or the same as that of thefirst-stage humidification chamber 16; and the bath 24 in each of thehumidification chambers 16, 18, 20 and 22 can have a width (w) that issubstantially greater than (e.g., at least twice as great as) its height(h) to enhance the efficiency with which the vaporizable component isvaporized and transferred to the carrier gas. The pressure drop on thecarrier-gas (bottom) side of the sparger plate 40 is a strong functionof the height of the bath 24 because the hydrostatic height of the bath24 needs to be overcome by the air to keep the bath liquid from“weeping” through the sparger plate 40 to the stage below. A mainadvantage of the low height of the bath 24 is, hence, the reducedelectricity consumption in the air-moving device (blower) 34 because ofthe lower pressure drop. Maintaining a low height of the bath is alsofeasible in this context because the characteristic dimension of heattransfer is of the order of a few millimeters.

An embodiment in which a multi-stage bubble-column humidifier 12 anddehumidifier 48 are stacked is illustrated in FIG. 3. In thisembodiment, the humidifier 12 includes four stages 16, 18, 20 and 22 andoperates as described in the embodiments, above. Here, however, thedehumidified carrier gas 66 from the fourth-stage humidification chamber22 is pumped from the fourth-stage humidification chamber 22 into thefirst-stage dehumidification chamber 50 of the dehumidifier 48. Thedehumidifier 48 can have the same or essentially the same design as themulti-stage bubble-column dehumidifier of U.S. application Ser. No.13/241,907. The baths 58 in the dehumidification chambers 50, 52, 54,and 56 can be formed of a liquid having the same composition (e.g.,water) as the component vaporized from the feed liquid in the humidifier12.

Among the dehumidification chambers 50, 52, 54 and 56, the temperatureof the bath 58 in the first-stage dehumidification chamber 50 is higherthan the temperature of the bath 58 in the second-stage dehumidificationchamber 52; the temperature of the bath 58 in the second-stagedehumidification chamber 52 is higher than the temperature of the bath58 in the third-stage dehumidification chamber 54; and the temperatureof the bath 58 in the third-stage dehumidification chamber 54 is higherthan the temperature of the bath 58 in the fourth-stage dehumidificationchamber 56. Pure condensed liquid (e.g., liquid water) is extracted fromthe dehumidifier 48 via output conduit 76 into which the condensateflows from each of the dehumidification chambers 50, 52, 54 and 56.

The baths 58 can be heated by thermal energy transferred from the hothumidified carrier gas 66 successively injected into and through each ofthe baths 58, where the condensable vapor component is condensed fromthe humidified carrier gas 66 in liquid form into the baths 58 as thecarrier gas 66 is successively cooled through the stages. Meanwhile, thefeed liquid is pumped from the feed-liquid source 14 through aserpentine conduit 60 that snakes through the bath 58 in each stage;thermal energy is conducted from the baths 58 through the conduit 60into the feed liquid to gradually pre-heat the feed liquid en route to aheater 62 that injects additional thermal energy 70 into the feed liquidto raise its temperature, e.g., to 70° C. before the feed liquid isinjected into the fourth-stage humidification chamber 22 to form thebath 24 therein.

In the embodiment of FIG. 4, the apparatus also includesmulti-extraction conduits 72 and 74 extending between intermediatelocations (i.e., locations between the initial and final chambers) inthe multi-stage humidifier 12 and dehumidifier 48. Conduit 74 extracts aportion of the feed-liquid remnant from the fourth-to-third-stageconduit 26 (though it can also/alternatively extract from conduit 28 or30) and recirculates the extracted feed-liquid remnant (at a warmertemperature) back to the feed-liquid conduit 60 between stages (here,between the first- and second-stage dehumidification chambers 50 and 52)of the multi-stage dehumidifier 48. With multi-extraction, theextraction/injection of the feed liquid from in-between the stages ofthe bubble column(s) via conduits 72 facilitates thermodynamic balancingof the system in operation. Similarly, a portion of the carrier gas canbe extracted from at least one intermediate location in the humidifier12 (here, from second-stage humidification chamber 28) via conduit 74and injected into a stage (here, into the second-stage dehumidificationchamber 52) of the multi-stage dehumidifier 12.

In describing embodiments of the invention, specific terminology is usedfor the sake of clarity. For the purpose of description, specific termsare intended to at least include technical and functional equivalentsthat operate in a similar manner to accomplish a similar result.Additionally, in some instances where a particular embodiment of theinvention includes a plurality of system elements or method steps, thoseelements or steps may be replaced with a single element or step;likewise, a single element or step may be replaced with a plurality ofelements or steps that serve the same purpose. Further, where parametersfor various properties or other values are specified herein forembodiments of the invention, those parameters or values can be adjustedup or down by 1/100^(th), 1/50^(th), 1/20^(th), 1/10^(th), ⅕^(th),⅓^(rd), ½, ⅔^(rd), ¾^(th), ⅘^(th), 9/10^(th), 19/20^(th), 49/50^(th),99/100^(th), etc. (or up by a factor of 1, 2, 3, 4, 5, 6, 8, 10, 20, 50,100, etc.), or by rounded-off approximations thereof, unless otherwisespecified. Moreover, while this invention has been shown and describedwith references to particular embodiments thereof, those skilled in theart will understand that various substitutions and alterations in formand details may be made therein without departing from the scope of theinvention. Further still, other aspects, functions and advantages arealso within the scope of the invention; and all embodiments of theinvention need not necessarily achieve all of the advantages or possessall of the characteristics described above. Additionally, steps,elements and features discussed herein in connection with one embodimentcan likewise be used in conjunction with other embodiments. The contentsof references, including reference texts, journal articles, patents,patent applications, etc., cited throughout the text are herebyincorporated by reference in their entirety; and appropriate components,steps, and characterizations from these references may or may not beincluded in embodiments of this invention. Still further, the componentsand steps identified in the Background section are integral to thisdisclosure and can be used in conjunction with or substituted forcomponents and steps described elsewhere in the disclosure within thescope of the invention. In method claims, where stages are recited in aparticular order—with or without sequenced prefacing characters addedfor ease of reference—the stages are not to be interpreted as beingtemporally limited to the order in which they are recited unlessotherwise specified or implied by the terms and phrasing.

What is claimed is:
 1. A method for humidification of a vaporizablecomponent from a feed liquid into a carrier gas, the method comprising:flowing the feed liquid including the vaporizable component into asecond-stage humidifier chamber of a multi-stage humidifier to form asecond-stage humidifier bath at a second humidification temperature;flowing a first remnant of the feed liquid from the second-stagehumidifier chamber into a first-stage humidifier chamber of themulti-stage humidifier to form a first-stage humidifier bath at a firsthumidification temperature, wherein the first humidification temperatureis lower than the second humidification temperature, wherein thefirst-stage humidifier bath is separated from the second-stagehumidifier bath via a sparger plate; removing a second remnant of thefeed liquid from the first-stage humidifier chamber; injecting thecarrier gas into the first-stage humidifier bath in the first-stagechamber and bubbling the carrier gas through the feed liquid in thefirst-stage humidifier bath, where the carrier gas collects thevaporizable component in vapor form from the first remnant of the feedliquid to partially humidify the carrier gas with the vaporizablecomponent, and wherein a top gas region comprising the partiallyhumidified carrier gas forms above the first-stage humidifier bath inthe first-stage humidifier chamber; flowing the partially humidifiedcarrier gas from the top gas region of the first humidifier chamberdirectly through the sparger plate into the second-stage humidifier bathin the second-stage humidifier chamber and bubbling the carrier gasthrough the second-stage humidifier bath, where the carrier gas collectsmore of the vaporizable component in vapor form from the feed liquid tofurther humidify the carrier gas with the vaporizable component, whereinthe partially humidified carrier gas in the top gas region of thefirst-stage humidifier chamber has a pressure greater than a hydrostaticpressure of the second-stage humidifier bath, and wherein the first- andsecond-stage humidifier baths maintain a majority liquid phase when thecarrier gas is bubbled through the baths; and removing the humidifiedcarrier gas from the second-stage humidifier chamber.
 2. The method ofclaim 1, wherein the feed liquid that flows into the second-stagehumidifier chamber is a remnant of a liquid from a third-stagehumidifier bath at a third humidification temperature in a third-stagehumidifier chamber, wherein the third humidification temperature ishigher than the second humidification temperature, the method furthercomprising directing the humidified carrier gas from the second-stagehumidifier chamber into the third-stage humidifier bath in thethird-stage humidifier chamber and bubbling the humidified carrier gasthrough the third-stage humidifier bath, where the humidified carriergas is further humidified with more of the vaporizable component invapor form from the third-stage bath.
 3. The method of claim 1, whereinthe multi-stage humidifier is an integral structure, wherein thepartially humidified carrier gas passes directly from the first-stagehumidifier chamber through the sparger plate into the second-stagehumidifier bath in the second-stage humidifier chamber without exitingthe integral structure.
 4. The method of claim 3, wherein the stages areseparated only by the sparger plate.